Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!

Valve Authority

The valve authority expresses the ratio between pressure drop across the control valve compared to total pressure drop across the whole system.

Valve authority - pressure drop in circuit

Control valve authority can be expressed as

N = dpv / (dpv + dpc)                          (1)


N = valve authority

dpv = pressure drop across a full open control valve (psi, Pa, kPa, bar)

dpc = pressure drop across the circuit (psi, Pa, kPa, bar)

To obtain control it is recommended that the control valve size is selected so that its authority is never less than 0.5. In general valve authority between

  • 0 - 0.25 -> unstable to fair control
  • 0.25 - 0.5 -> fair to good control
  • 0.5 - 1.0 -> good control

Example - Control Valve Authority in a Heating System

The total pressure drop in a heating system circuit at full load is 15 kPa. The volume flow is 1.4 l/s.

For decent control the valve authority is set to N = 0.8. The pressure drop across the control valve dpv can be calculated by transforming (1) to

dpv = N dpc / (1 - N)                     (1b)

- or with values

dpv = 0.8 (15 kPa)  / (1 - 0.8)

     = 60 kPa

The flow factor for the valve with volume flow 1.4 l/s can be estimated to approximately

Kv = 7

by using this flow factor diagram. For a Straight Through Diaphragm Valve of "Saunders" type this corresponds to a 15 mm valve.

Related Topics

  • Control Valve Sizing

    Control Valve terminology, bodies, trim, flow characteristics, Cv and Kv sizing, noise, actuators, positioners and more.

Related Documents


Search is the most efficient way to navigate the Engineering ToolBox.

Engineering ToolBox - SketchUp Extension - Online 3D modeling!

3D Engineering ToolBox Extension to SketchUp - add parametric components to your SketchUp model

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with older versions of the amazing SketchUp Make and the newer "up to date" SketchUp Pro . Add the Engineering ToolBox extension to your SketchUp Make/Pro from the Extension Warehouse !

Translate this Page

Translate this page to Your Own Language .

About the Engineering ToolBox!

Privacy Policy

We don't collect information from our users. More about

We use a third-party to provide monetization technologies for our site. You can review their privacy and cookie policy here.

You can change your privacy settings by clicking the following button: .


This page can be cited as

  • The Engineering ToolBox (2008). Valve Authority. [online] Available at: [Accessed Day Month Year].

Modify the access date according your visit.

3D Engineering ToolBox - draw and model technical applications! 2D Engineering ToolBox - create and share online diagram drawing templates! Engineering ToolBox Apps - mobile online and offline engineering applications!

Unit Converter